1. Field of the Invention
The present invention relates to a laminated electronic component and a method for manufacturing the same, and more particularly, to a laminated electronic component, which has external electrodes directly formed on external surfaces of a laminate by plating, and to a method for manufacturing the same.
2. Description of the Related Art
As shown in FIG. 4, a laminated electronic component 101, defined by a laminated ceramic capacitor, includes a laminate 105 including insulating layers 102, which are laminated to each other and which are made, for example, of a dielectric ceramic, and layer-shaped internal electrodes 103 and 104 which are disposed along interfaces between the insulating layers 102. Ends of the internal electrodes 103 and ends of the internal electrodes 104 are exposed at one end surface 106 and the other end surface 107 of the laminate 105, respectively, and external electrodes 108 and 109 are provided so as to electrically connect the ends of the internal electrodes 103 and the ends of the internal electrodes 104, respectively.
When the external electrodes 108 and 109 are formed, paste electrode layers 110 are first formed by applying a metal paste including a metal component and a glass component on the end surfaces 106 and 107 of the laminate 105, followed by firing. Next, on the paste electrode layers 110, first plating layers 111 primarily composed, for example, of Ni are formed, and second plating layers 112 primarily composed, for example, of Sn are further formed thereon. That is, each of the external electrodes 108 and 109 has a three-layered structure including the paste electrode layer 110, the first plating layer 111, and the second plating layer 112.
When the laminated electronic component 101 is mounted on a substrate using solder, the external electrodes 108 and 109 must have good wettability to the solder. At the same time, the external electrode 108 is required to electrically connect the internal electrodes 103, which are electrically insulated from each other, and the external electrode 109 is required to electrically connect the internal electrodes 104, which are electrically insulated from each other. The second plating layer 112 ensures good solder wettability, and the electrical connection of the internal electrodes 103 and that of the internal electrodes 104 are performed by the respective paste electrode layers 110. The first plating layer 111 functions to prevent solder leaching during solder bonding.
However, the paste electrode layer 110 has a relatively large thickness of several tens to several hundreds of micrometers. Thus, when this laminated electronic component 101 is formed to have predetermined standard dimensions, in order to ensure the volume of the paste electrode layers 110, an effective volume necessary to obtain electrostatic capacitance must be unfavorably decreased corresponding to the volume of the paste electrode layers 110. On the other hand, since the thicknesses of the plating layers 111 and 112 are each approximately several micrometers, when the external electrodes 108 and 109 are defined by only the first plating layer 111 and the second plating layer 112, a larger effective volume necessary to obtain electrostatic capacitance can be obtained.
For example, in Japanese Unexamined Patent Application Publication No. 2004-146401, a method is disclosed in which a conductive paste is applied to at least edge portions of end surfaces of a laminate in the lamination direction of internal electrodes so as to be in contact with extraction portions of the internal electrodes, this conductive paste is then formed into conductive films by firing or heat-curing, and electroplating is further performed on the end surfaces of the laminate to form electroplating films so as to be connected to the conductive films on the edge portions. According to this method, the thickness of the external electrode at the end surface can be decreased.
In addition, in Japanese Unexamined Patent Application Publication No. 63-169014, a method is disclosed in which conductive metal films are deposited by electroless plating on entire sidewall surfaces of a laminate at which internal electrodes are exposed so that the internal electrodes exposed at each sidewall surface are short-circuited to each other.
However, since plating is directly performed on the exposed ends of the internal electrodes by the external electrode-forming methods disclosed in Japanese Unexamined Patent Application Publication No. 2004-146401 and Japanese Unexamined Patent Application Publication No. 63-169014, a plating liquid which penetrates into the laminate along interfaces between the internal electrodes and insulating layers erodes the internal electrodes and/or a ceramic forming the insulating layers, and as a result, structural defects may occur. In addition, due to the defects described above, the reliability of a laminated electronic component, such as degradation in moisture load resistance properties, is degraded.